1. Field of the Invention
The present invention relates to a toner for use in an image forming method, such as an electrophotographic method, an electrostatic recording method or a toner jet method.
2. Related Background Art
As a binder resin for toner, a polycondensation resin such as polyester resin and a vinyl-type resin such as styrene-type resin have been employed principally. The polyester resin has an advantage of being excellent in the fixing property, but is difficult to make in a high molecular weight, and has a drawback of easily causing an offset phenomenon at a high temperature.
However, when a crosslinking component is added, in order to avoid such drawbacks, in the polyester resin for elevating the melt viscosity of resin and improving the high-temperature offset resistance, there result deteriorations not only in the fixing property but also in the pulverizing property at the toner manufacture.
On the other hand, the vinyl-type resin such as styrene-type resin is excellent in the pulverizing property at the toner manufacture and in the high-temperature offset resistance because a high molecular weight can be easily attained, but the blocking property and the developing property tend to be deteriorated in a lower molecular weight or a lower Tg for improving the fixing property.
Also various methods of using these two resins in a mixture have been investigated, in order to effectively exploit the advantages of these resins and to cover the drawbacks thereof.
Japanese Patent Application Laid-open No. S54-114245 discloses a toner containing a mixed resin of a polyester resin and a vinyl-type resin. However, the polyester resin and the vinyl-type resin are basically poor in the mutual solubility, and a colorant or a wax added to the toner shows insufficient dispersibility, thus tending to result in an insufficient developing property.
Japanese Patent Application Laid-open No. S56-116043 discloses a toner comprising a polymer obtained by polymerizing a vinyl-type monomer in the presence of a reactive polyester resin, but the content of the polyester resin is low with respect to the vinyl-type monomer, thus showing little improving effect on the fixing property.
Japanese Patent Application Laid-open No. S58-159546 discloses a toner comprising a polymer obtained by polymerizing an styreneacrylic monomer in the presence of a saturated polyester resin. However, for improving the fixing property and the high-temperature offset resistance, a control is essential on the molecular weight distribution of the binder resin, the mere polymerization of a styreneacrylic monomer in the presence of a saturated polyester resin is insufficient.
Japanese Patent Application Laid-open No. S58-102246 discloses a toner comprising a polymer obtained by polymerizing a styreneacrylic monomer in the presence of an unsaturated polyester resin. However, with respect to the vinyl-type monomer, the amount of polyester resin is as low as 99.5:0.5 to 91:9, thus showing little improving effect on the fixing property.
Japanese Patent Application Laid-open No. H01-156759 discloses a toner containing, as the binder resin, a graft polymer which is obtained by graft polymerization of a vinyl-type monomer to an unsaturated polyester resin and which has a weight-average molecular weight of 8,000 to 20,000, a melt viscosity at 100° C. of 104 to 106 poise, and a glass transition temperature of 50 to 75° C. However, for further improvements in the fixing property and the high-temperature offset resistance, a more precise control on the molecular weight distribution of the toner is necessary.
Japanese Patent Application Laid-open No. H02-881 discloses a toner comprising a polymer obtained by esterifying a styrene-type resin having acid group and a polyester resin. In such method, though the mutual solubility of the polyester resin and the vinyl-type copolymer can be improved, but the content of the gel component and the molecular weight of the vinyl-type resin component contained in the gel component are not controlled, so that it is insufficient for satisfying the fixing property and the high-temperature offset resistance at a higher level.
Japanese Patent Application Laid-open No. H11-153885 discloses a binder for electrophotographic toner, obtained by reacting a non-linear polyester having a weight-average molecular weight (Mw) of 5,000 to 200,000, and a ratio (Mw/Mn) of weight-average molecular weight (Mw) and number-average molecular weight (Mn) of 3 to 50, and a vinyl-type polymer. In this method, since the vinyl-type polymer and the polyester polymer are hybridized by an esterification reaction, a higher reaction temperature is required for obtaining a higher hybridization rate, and the vinyl-type polymer may be decomposed by heat. At a temperature not decomposing the vinyl-type polymer, the esterification reaction does not proceed sufficiently, so that a sufficient hybridization is difficult to attain, whereby the fixing property, high-temperature offset resistance and developing property are difficult to satisfy.
Also various proposals have been made referring to the molecular weight distribution of a component soluble in tetrahydrofuran (THF) in the toner.
Japanese Patent Application Laid-open No. H09-6050 discloses a relationship, in a component with a molecular weight of 50,000 or less in the GPC molecular weight distribution of a THF-soluble matter in the toner binder resin, between a weight-average molecular weight measured by a light scattering method and a weight-average molecular weight measured by a GPC method. However, such limitation on the low molecular side does not take into consideration a mixing property of the low molecular weight component and the high molecular weight component. As the low-temperature fixing property and the offset resistance are mutually contradictory in a sense, improvement is still insufficient in the low-temperature fixing property while maintaining the high-temperature offset resistance.
Japanese Patent Application Laid-open No. H09-146305 discloses, in the toner binder resin within a molecular weight range of 2,000 to 100,000, a relationship between a weight-average molecular weight measured by the light scattering method and an inertial radius. Also Japanese Patent Application Laid-open No. H09-106102 defines, in components of the GPC-measured molecular weight ranges of 2,000 to 50,000 and 100,000 or higher, a relationship between a weight-average molecular weight measured by the light-scattering method and an inertial radius. However, in recent high-speed image forming apparatuses, such branched structure cannot be considered optimum, and a branched structure capable of achieving the fixing performance in a wider temperature range has to be proposed anew. Also in consideration of the dispersibility between the binder resin and other materials such as a releasing agent at the toner manufacture, the branched structure in the component of the high molecular weight range still has a room for further consideration.
Thus, further improvements in the fixing property, high-temperature offset resistance and developing property are required, and the development of a better toner is strongly desired.